CN101863476A

CN101863476A - Method for removing boron element from silicon

Info

Publication number: CN101863476A
Application number: CN200910111524A
Authority: CN
Inventors: 郑智雄; 张伟娜; 胡满根; 戴文伟
Original assignee: NANAN SANJING SUNSHINE AND POWER Co Ltd
Current assignee: NANAN SANJING SUNSHINE AND POWER Co Ltd
Priority date: 2009-04-17
Filing date: 2009-04-17
Publication date: 2010-10-20
Anticipated expiration: 2029-04-17
Also published as: CN101863476B

Abstract

The invention discloses a method for removing boron element from silicon and relates to the field of semiconductor materials. The method comprises the following steps of: by taking advantages of the characteristics of silicon alloy, mixing silicon and a metal capable of dissolving boron when the metal is in a liquid state in a proportion, melting the mixture under vacuum, directionally solidifying the mixture, slowly cooling the mixture, and when the silicon is solidified but the metal is not solidified, pouring out the liquid metal and the boron dissolved in the metal. Because the metal capable of dissolving boron is adopted to dilute impurities in the silicon, the method of the invention can effectively reduce the impurity content of the silicon, particularly the boron content, and B content in solid silicon can be reduced to over 70 percent.

Description

A kind of method of removing boron in the silicon

Technical field

The present invention relates to field of semiconductor materials, relate to the method for purification of from Pure Silicon Metal, removing boron.

Background technology

Polysilicon is the base mateiral of solar cell, is the new high-tech industry of state key encourage growth, and the demand to polysilicon increases year by year both at home and abroad, and presents the phenomenon that supply falls short of demand.The main technique of producing the solar battery grade crystalline silicon at present in the world is the improvement Siemens Method, it comprises reduction furnace tail gas recycle technology that the trichlorosilane purification techniques that removes boron, large-scale reduction furnace technology, hydrogen and hydrogen chloride gas reclaim, hydrogenation of silicon tetrachloride technology etc., manufacturing process comprises chlorination-reduction-processes such as deposition, and is very complicated.The main raw material that uses during production is industrial silicon, liquid chlorine, hydrogen etc.

Generally believe that at present using cheap industrial silicon to prepare solar-grade polysilicon is one of effective means that reduces cost.In order to reduce manufacturing cost, use the low-purity silicon materials to make solar cell is the target that people pursue always.The purity target of physics manufactured polysilicon is a solar level, and it has less investment, and energy consumption is low, and advantages such as environmentally safe are to satisfy the demand of fast-developing photovoltaic industry.

For guaranteeing needed photoelectric transformation efficiency, the content of impurity elements such as the phosphorus in the silicon, boron, carbon must be very low, wherein boron generally will be at 0.1-0.3ppm, in the metallurgical industry during finishing metal silicon, utilize the segregation coefficient of metallic element to be significantly less than 1 character, can remove impurity by directional freeze, but the segregation coefficient of silicon and boron approaches 1, therefore solidify refining and have any problem.

Summary of the invention

The method that the purpose of this invention is to provide boron in a kind of effective reduction silicon.

A kind of method of removing boron in the silicon the steps include:

Step 1: the metal or alloy 55-45wt of solubilized boron puts into the high purity graphite crucible during with polysilicon 45-55wt and liquid state;

Step 2: after vacuumizing in the stove, feed rare gas element;

Step 3: be warming up on the fusing point of silicon and metal, be incubated 1h at least;

Step 4: open temperature control, be cooled under the fusing point of silicon and metal, directional freeze is progressively cooled off with 0.01-0.05 ℃/h, makes the abundant fractional condensation of silicon, aluminium and silumin in the crucible;

Step 5: the silicon crystallisation process after finishing is poured out liquid aluminium.

Described metal is that fusing point is lower than 1400 ℃, and the metal or alloy of solubilized boron when liquid, and like this, when silicon fused with metal mixture, the boron in the silicon dissolved in this metal or alloy; Along with solution cooling, treat that silicon solidifies, and metal is not when solidifying, make liquid metal by flowing out in the crucible, because boron is dissolved in the liquid metal always, until pouring out, so can reach the purpose of purified silicon.

The fine powder of boron dissolves in the nitric acid and sulfuric acid of heat, also dissolves in most melt metal, as copper, iron, magnesium, calcium, aluminium etc.In a preferred embodiment of the present invention, described metal is Al.Aluminium can be removed when liquid state, also can remove when solid-state.

The described rare gas element of step 3 is argon gas or helium.

The described soaking time of step 3 is 2h-3h.

By the above-mentioned description of this invention as can be known, compare with prior art, the present invention has adopted the impurity in the metal pair silicon of solubilized boron to filter, and method of the present invention can effectively reduce foreign matter content in the silicon, particularly boron impurity content can drop to the B content in the solid silicon more than 70%.The present invention adopts cheap aluminium, silicon purified, and the product of gained of the present invention, a part is the silicon after purifying, and another part is a silumin, and silumin is the forged material commonly used in the aircraft industry, and is also of many uses in other field.

Description of drawings

Fig. 1: reinforced stage synoptic diagram, its middle and lower part 2 is the silicon material of boracic, top 1 is aluminium;

Fig. 2: high temperature mixed smelting stage synoptic diagram, aluminium and silicon mix fusion;

Fig. 3, cooling fractional condensation stage synoptic diagram: bottom 6 is a silicon, and middle part 5 is a silumin, and top 4 is aluminium, and the point in 4 is represented B impurity.

Embodiment

Embodiment 1

100kg puts into the high purity graphite crucible with the 4-5N polysilicon, puts into Al 100kg simultaneously, vacuumizes the back and feeds argon shield, is warming up to 1100 ℃ of silicon and Al mixture and all is molten into liquid state, insulation 1h.Open temperature control then, the material in the crucible is progressively cooled off, the type of cooling is directed fixing slowly cooling, and speed of cooling is 0.05 ℃/h.Make the abundant fractional condensation of silicon, aluminium and silumin.After fractional condensation finished, silumin accounted for 50%wt, and liquid aluminium accounts for 6.3%wt, and solid state si accounts for 43.7%wt.Boron descends more than 70% in the solid state si of separation back.

Embodiment 2

90kg puts into the high purity graphite crucible with the 4-5N polysilicon, puts into Al 110kg simultaneously, vacuumizes the back and feeds argon shield, is warming up to 1100 ℃ of silicon and Al mixture and all is molten into liquid state, insulation 1h.Open temperature control then, the material in the crucible is progressively cooled off, the type of cooling is directed fixing slowly cooling, and speed of cooling is 0.03 ℃/h.Make the abundant fractional condensation of silicon, aluminium and silumin.After fractional condensation finished, silumin accounted for 50%wt, and liquid aluminium accounts for 6.3%wt, and solid state si accounts for 43.7%wt.Boron descends more than 70% in the solid state si of separation back.

Embodiment 3

110kg puts into the high purity graphite crucible with the 4-5N polysilicon, puts into Al 90kg simultaneously, vacuumizes the back and feeds argon shield, is warming up to 1100 ℃ of silicon and Al mixture and all is molten into liquid state, insulation 1h.Open temperature control then, the material in the crucible is progressively cooled off, the type of cooling is directed fixing slowly cooling, and speed of cooling is 0.01 ℃/h.Make the abundant fractional condensation of silicon, aluminium and silumin.After fractional condensation finished, silumin accounted for 50%wt, and liquid aluminium accounts for 6.3%wt, and solid state si accounts for 43.7%wt.Boron descends more than 70% in the solid state si of separation back.

Above-mentioned only is specific embodiments of the invention, but design concept of the present invention is not limited thereto, and allly utilizes this design that the present invention is carried out the change of unsubstantiality, all should belong to the behavior of invading protection domain of the present invention.

Claims

1. a method of removing boron in the silicon the steps include:

Step 1: the metal or alloy weight part 45-55 of solubilized boron puts into the high purity graphite crucible during with polysilicon weight part 45-55 and liquid state;

Step 2: after vacuumizing in the stove, feed rare gas element;

2. a kind of method of removing boron in the silicon as claimed in claim 1 is characterized in that: the described polysilicon purity of step 1 is 4-5N.

3. a kind of method of removing boron in the silicon as claimed in claim 1 is characterized in that: described metal or alloy fusing point is lower than 1400 ℃.

4. a kind of method of removing boron in the silicon as claimed in claim 2 is characterized in that: described metal is Al.

5. a kind of method of removing boron in the silicon as claimed in claim 1 is characterized in that: the described rare gas element of step 3 is argon gas or helium.

6. a kind of method of removing boron in the silicon as claimed in claim 1 is characterized in that: the described soaking time of step 3 is 2h-3h.